An arrangement is known (German DT-OS No. 1,807,639) in which the piston exposed to the combustion process is cooled by lubricant taken from the lubricating circuit. For this purpose a cooling oil pipe leading to the piston is connected through a spring-loaded valve to the lubricating oil circuit, this valve only opening when the oil pressure reaches a predetermined level, which is achieved at a predetermined speed of the lubricating oil pump connected to the engine. In this way, particularly in the lower speed range, unwanted excessive cooling of the piston is avoided and the lubricating oil pressure is maintained at a level sufficient for supplying the lubricating circuit feeding the components that require lubrication.
In such an arrangement, however, after a cold start the cold and accordingly viscous nature of the lubricating oil can lead to an increase in the pressure of the oil so that the spring-loaded valve opens even at a low engine speed and already results in the piston being cooled under these operating conditions. However unwanted cooling of the piston also occurs when running at a higher speed after a cold start. This cooling of the piston, however, significantly delays the attainment of the operating temperature so that in this phase of operation there is an increase in the fuel consumption and unfavorable exhaust gas conditions arise. Moreover, as the lubricating oil circuit is also fed through an oil cooler the warming up phase can experience a further delay, in particular at low external temperatures. A further drawback lies in the fact that when the engine is hot, both under idling conditions and also at high loads and low speeds, no cooling of the piston, necessary in itself, can take place as the lubricant pressure under these conditions of operation is not sufficient for supplying the piston cooling.